This invention relates to an apparatus for expanding the capacity of a serial data bus, such as the Milbus 1553, Stanag 3838 and others.
Data buses of this type, particularly the Milbus Mil-STD 1553, are considered as so-called standard elements in the military. A data bus of this type permits the use of serial data buses as a communications medium between different subsystems up to a maximum of 32. The journal Design & Electronik, 3rd Edition, of Feb. 7, 1989 also discusses this Milbus according to MIL-STD 1553.
The above-mentioned state of the art Milbuses comprise, among other things, a two-wire bus to which the bus controller and up to 32 general remote terminals (RT's) may be connected by way of stubs. Often two redundant buses are designed in parallel so as to be able to switch to the second bus in the case of disturbances. Such redundant buses are commonly referred to as bus A and bus B.
The limitation to 32 RT's is the result of the number of the available addresses, and the fact that only one RT can be connected to each of the respective stubs. Nevertheless, certain applications may require connection of additional remote terminals to the bus. Problems occur, however, in the expansion of existing systems if all 32 RT addresses have been allocated or if, for the connection of additional RT's, when the bus configuration has been established, no more access can be created to the actual bus, and therefore a connection to an already used stub must take place.
In principle, it is possible to solve this problem by using a standard RT with a standard bus controller BC. The RT is operated on the stub of the Milbus and transmits data (commands) to the bus controller (BC) of another Milbus. Up to 32 RT's may then be connected to this secondary Milbus.
The disadvantage of this solution is, however, that all data/commands must first be completely received by the RT-BC apparatus and only then can be actively transmitted to the secondary Milbus. As a result, too much time may be lost to accommodate time critical applications--which are frequent in the military sector. Furthermore, errors which occur on the second Milbus require special handling because no transparent access exists to the connected RT or RT's.
It is an object of the present invention to provide an apparatus of the initially mentioned type by which the above-mentioned disadvantages of the state of the art are eliminated, and by which a transparent connection of several RT's to one RT-address (to one stub) with almost no delay is made possible.
This object is achieved by the Milbus repeater according to the invention, in which the bus controller unit for the second Milbus is replaced by so-called transparent hardware logic, described in detail hereinafter. This hardware logic transmits the Milbus traffic from the primary bus almost without any loss of time directly to the secondary bus and vice versa. Because the address of the general remote terminal RT of the Milbus repeater will now be identical with the address of an RT connected to the secondary Milbus, additional logic circuitry is provided in order to control the distribution of data.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.